Abstract: 【Objective】 Resistance of 68 major wheat cultivars, each of which is planted at least over 70 thousand hectares yearly in China, to powdery mildew was analyzed based on resistance frequencies to mildew population from different provinces/ autonomous regions and whole China in order to evaluate the risks of mildew epidemics. Their resistance genes were also postulated.【Method】1 094 wheat single colony powdery mildew isolates were collected from 12 provinces (autonomous region) which grow wheat in China in the spring of 2011. Resistance frequencies of 68 cultivars were estimated by the mean of inoculating detached leaves segments of each cultivar with 1 094 isolates, respectively. Cluster analysis was carried out with UPGAMA (unweighted pair group arithmetic mean analysis) model of the software NTSYSpc2.10e based on the phenotypic resistance data. Resistance genes of the 68 cultivars were postulated by comparing resistance spectra of the cultivars to 31 differential isolates with those of materials possessing known resistance genes to the isolates. 【Result】 The resistance spectrum of each cultivar differed significantly from that of others. Resistance frequencies of Neimai8, Neimai9 and Mianmai37 were higher than 99%, while those of Jimai22, Yangmai11, Yangmai12, Yangmai13 and Lunxuan987 were between 70% and 90%. Among the 68 cultivars, 54 cultivars counting for 79.4%, had resistance frequencies lower than 40%, suggesting the resistance of these cultivars had been overcome. The resistance frequency of a cultivar to mildew population from the region where the cultivar was grown was lower than that to the mildew population from the region where the cultivar was not grown. Cluster analysis indicated 68 cultivars could be classified into four groups. Group one included 6 cultivars and out of them, resistance frequencies of 5 cultivars to all isolates were between 40% and 70%. Group two included 7 cultivars with resistance frequencies higher than 70%. Group three composed of 54 cultivars with resistance frequencies lower than 40%. The fourth group had only one cultivar with resistance frequency of 46.1%. The cultivars came from the same province and the cultivars with the similar resistance frequency had been clustered to the same group. It showed that they may have a similar resistance genetic background. Results of Pm postulation showed that Neimai8 and Neimai9 contains Pm21, Yanzhan4110, Xinmai208 and Yangmai11 possess Pm4b, Jimai22 possesses Pm2+ta, while the rest cultivars contain other unknown resistance factor(s) which could not be postulated. 【Conclusion】Nearly 80% of the cultivars wildly grown in China have a lower resistance frequency to wheat powdery mildew population. Referring to a cultivar, it was vulnerable to mildew population from the area where the cultivar is grown. There would be a risk of wheat powdery mildew epidemic if weather and other conditions favor for mildew epidemic. Many cultivars from the same region were clustered into the same group, it indicated that the resistance heterogeneity is lower in wheat grown in the region.

Key words: wheat powdery mildew , major wheat cultivars , resistance frequency , resistance gene